The flow of sand into producing oil and gas wells from the producing formations is well known. The best current sand control practice involves placement of gravel screens in the well in the vicinity of the production zone and packing gravel around the screen and into the formation openings to retard the entrainment of sand by fluids migrating to the well bore.
Gravel packing is usually done by the crossover method. The crossover method involves lowering a gravel screen below a crossover device and a packer to the payzone area on a working pipe string. The packer is closed against the well bore wall, and the gravel (usually in a viscous carrier fluid, or slurry) is pumped down the work string flow bore and dumped in the well annulus outside the screen below the packer. The carrier fluid is allowed to return through the screen into a stinger washpipe extending into the screen interior, back to the crossover means, where it is directed into the well bore above the packer.
Hardware has evolved that allows the work string to control the packer, crossover device, and release the screen from the work string, so that the screen is left in the well, and most other hardware is recovered with the work string.
Advantages of the crossover system includes confinement and control of the downflowing gravel slurry within the work string to prevent contamination of the upper well bore with gravel and debris dislodged by gravel.
When packers and gravel screen release contrivances are both used on one work string, the manner of setting the packer and releasing the screen should be separate, so that packer manipulations do not also release the screen. By using work string rotation and weight to set the packer and hydraulic pressure to release the screen, several operations can be carried out in one trip into the well with the work string. Flow through the work string is essential to several well-conditioning operations, and it is desirable to flow without releasing the screen. It is common practice to drop an object down the work string bore to prepare downhole machine elements to release screens on the next occurrence of forward circulation through the work string bore.
Prior art in releasing tools downhole without rotating the work string is typified by U.S. Pats. Nos. 2,409,811 and 4,175,778; the latter being specific for gravel packing and the former being more general in nature.
The screen release apparatus most closely related to the present invention is disclosed in U.S. Pat. No. 4,570,714. In terms of net effect, the present invention distinguishes in providing a forward or reverse circulation flow through channel to the very bottom of the screen assembly in communication with the work string flow bore prior to screen release and the ability to close the lower screen penetrating channel on screen release. The feature permits apparatus of the present invention to be used as if it were only a work string with a packer to reverse out sand and other materials without compromising the screens. Additionally, the present invention permits clean fluid to be used to backflush screens if they become plugged in well treating. Such actions are not possible with apparatus of the U.S. Pat. No. 4,570,714. It is quite possible to avoid one work string trip into the well with apparatus of the present invention.